1. 1 Exercise IC Field of View Objectives: Objectives: To measure the fields-of-view of the telescopes and Telrads used in this class To measure the fields-of-view of the telescopes and Telrads used in this class Topics: Topics: Magnification (M), Apparent Field (AF), True Field (TF) Results: Results: Calculate M and determine TF using both direct and star drift methods for several different eyepieces and compare results to theoretical values of TF

2. 2 Exercise IC Field of View The Field-of-View (FOV) is just the angular width of what can be seen The Field-of-View (FOV) is just the angular width of what can be seen – Eye: ~ 160 o – Binoculars: ~ 5 o – Telescopes: typically less than 1 o The True Field of a telescope depends on The True Field of a telescope depends on – Magnification from the eyepiece – Apparent Field of the eyepiece

3. 3 Exercise IC Field of View The True Field by calculation The True Field by calculation Eq. 1 Eq. 2

4. 4 Exercise IC Field of View The True Field by direct measure The True Field by direct measure Theory: Small Angle Formula Where  is in degrees and D and R are in the same units  D R

5. 5 Exercise IC Field of View Equipment needed: Equipment needed: – Telescope (Celestron-8) – Tape measure – A 2 to 2.5-meter strip of paper

6. 6 Exercise IC Field of View The True Field by direct measure Procedure: Take telescope outside or into Sewell Hall –S–S–S–Set up Telescope and aim towards a wall where you have taped down a 2 to 2.5 m strip of paper Telescope should be at least 25 meters from paper –F–F–F–Find edges of Field of View for the three “rings” of the Telrad bullseye (see white board) –F–F–F–Find Field of View of the 40-mm eyepiece and two other eyepieces (see white board) Compare results with the predicted (Calculated) values

7. 7 To calculate FOV using direct measurement Let  be the Field of View and solve for  in small angle formula Let  be the Field of View and solve for  in small angle formula – R is the distance to the target – D is the distance between marks on the paper hung on the wall Eq. 3  D R Telescope Marks Corresponding To one FOV

8. 8 The End

9. 9 Exercise IC Field of View The True Field by star drift method The True Field by star drift method – The sky drifts by at a rate of – Set up a telescope and put in an eyepiece – Find a star near the celestial equator – Put the star on the on the east edge of eyepiece field – Then turn off the clock drive and let the star drift across the field – Record the time ( T ) in seconds and calculate the field Eq. 3